[daip] solve for a complex band pass

[Eric Greisen]

Z.-Q. Shen writes:
 > Now, I decided to take two steps in deciding a complex bandpass.
 > First, using ac data to solve for the amplitude part  and then solve for
 > the phase part only by using xc data and fixing the amplitude solution.
 > This can be done in CPASS.
 > 
 > I have another question regarding the normalization (BPASSPRM(10)
 > in both BPASS and CPASS) and auto-normalization (CPARM(8) in CPASS).
 > I didn't see any difference with and without auto-normalization in
 > the CPASS run. Will such normalization (auto-scale) have any effect
 > on the amplitude?
 > 

Actually for VLBI when you use ACCOR you should do the normalization
since ACCOR should do all of the amplitude correction.  I too notice
that the CPASS solution is already normalized - and that CPASS does
not work correctly if you turn off all pre-solution normalizations
(i.e. set BPASSP(5)=1, CPARM(8) < 0 - the help file lies and 0 also
autonormalizes).

I noticed thatthe ac solutions for some antennas at the high channels
did not roll off the way the xc solutions did.  This is due to
aliasing from filters that do not roll off as they should.  In the xc
case, the fringe rotation acts against the aliased signal while there
is no suppresion in the ac case.  Thus, if you use the ac solution,
you should not trust your highest 10 or 20 channels.

Eric Greisen